A “B-Kit” is a standardized housing for optical assemblies, such as “Improved Forward-Looking Infrared” (IFLIR) assemblies, in military and other applications. The B-Kit is designed to be integrated with different “A-Kits” in a modular manner, with each A-Kit configured to be installed in a specific vehicle, such as M1, M2, M3, and BFIST tanks as well as the LRAS3 for various scout vehicles and other military vehicles. Accordingly, the limited interior space in a B-Kit housing places design constraints on optical assemblies used in the B-Kit. The optical assembly may have additional design constraints as well. For example, an IFLIR assembly for use with the B-Kit is required to have at least four parfocal fields-of-view (FOVs), including a wide field of view (WFOV), a medium field of view (MFOV), a narrow field of view (NFOV), and an ultra-narrow field of view (UNFOV). All four FOVs must be operable at an aperture of substantially F/4.0, and the WFOV, MFOV, and NFOV must also be operable at an aperture of substantially F/2.5. Thus, there is a need for an optical assembly that meets these parameters.